Common MIG Wire Classifications

ER70S-6 (Most Common)

• Deoxidizers: Manganese, silicon
• Tensile strength: 70,000 PSI minimum
• Best for: Dirty or rusty steel, single-pass welds, general fabrication
• Shielding gas: 75/25 Ar/CO₂ or 100% CO₂
• Spatter level: Moderate

ER70S-3

• Deoxidizers: Lower manganese and silicon than ER70S-6
• Tensile strength: 70,000 PSI minimum
• Best for: Clean steel, multi-pass welds, automotive sheet metal
• Shielding gas: 75/25 Ar/CO₂ (100% CO₂ not recommended)
• Spatter level: Low

ER308L (Stainless Steel)

• Composition: 19-21% chromium, 9-11% nickel
• Best for: 304/304L stainless steel
• Shielding gas: 90/10 Ar/CO₂ or tri-mix (He/Ar/CO₂)
• Corrosion resistance: Excellent

ER316L (Stainless Steel)

• Composition: 18-20% chromium, 11-14% nickel, 2-3% molybdenum
• Best for: 316/316L stainless, marine environments, chemical processing
• Shielding gas: 90/10 Ar/CO₂ or tri-mix
• Corrosion resistance: Superior (molybdenum addition)

Wire Diameter Selection

Rule of thumb: Thinner wire = better control on thin material. Thicker wire = faster deposition on heavy plate.

Shielding Gas Impact on Wire Performance

75/25 Argon/CO₂ (C25)

• Pros: Low spatter, smooth arc, good bead appearance
• Cons: Higher cost than 100% CO₂
• Best for: ER70S-3, ER70S-6, stainless steel

100% CO₂

• Pros: Deep penetration, low cost
• Cons: Higher spatter, rougher arc
• Best for: ER70S-6 on thick steel (not recommended for ER70S-3)

90/10 Argon/CO₂

• Pros: Minimal spatter, excellent for stainless
• Cons: Shallow penetration on carbon steel
• Best for: ER308L, ER316L stainless wire

Surface Condition Requirements

ER70S-6 advantage: Higher deoxidizers clean impurities during welding. ER70S-3 requires clean base metal to avoid porosity.

AWS Filler Metal Specifications

AWS A5.18 (Carbon Steel MIG Wire) – Covers ER70S-3, ER70S-6, and other carbon steel wires – Defines chemical composition, tensile strength, and elongation requirements

AWS A5.9 (Stainless Steel MIG Wire) – Covers ER308L, ER316L, and other stainless wires – Specifies corrosion resistance and ferrite content

Wire Storage & Handling

Moisture Contamination – Causes: Porosity, hydrogen cracking – Prevention: Store in sealed containers with desiccant packs – Shelf life: 12 months (carbon steel), 6 months (stainless)

Wire Feed Issues – Kinked wire = erratic arc and bird-nesting – Solution: Use proper spool tension and liner size

Liner Compatibility

Oversized liner = wire wander. Undersized liner = excessive friction and burnback.

Common Mistakes

Using ER70S-3 on rusty steel
Low deoxidizers can’t compensate for surface contamination. Result: porosity and weak welds. Use ER70S-6 or clean the base metal.

Wrong liner size for wire diameter
0.035” wire in 0.045” liner causes erratic feeding. Match liner to wire diameter within 0.005”-0.010”.

Storing stainless wire without moisture protection
Stainless wire absorbs moisture faster than carbon steel. Always use sealed containers with desiccant.

Buying Checklist

• ✓ Wire classification matches base metal (ER70S-6 for dirty steel, ER70S-3 for clean)
• ✓ Diameter suits material thickness and amperage range
• ✓ Shielding gas compatible with wire type
• ✓ AWS A5.18 or A5.9 certification marked on spool
• ✓ Liner size matches wire diameter
• ✓ Storage container includes moisture protection
• ✓ Spool size fits your machine (2 lb, 10 lb, 33 lb, 44 lb)